Fastening devices of this general type are well-known. They typically comprise a pin which is inserted into a surface of a first panel to a predetermined depth so that its head protrudes from the panel, and a rotatable locking drum positioned in a recess in a second panel and arranged to receive the head of the pin. The panels are fastened together by rotating the locking drum which, by means of internal camming surfaces, pulls the head of the pin inwardly thus drawing the two panels together.
These known devices have disadvantages in that vibration, for example during transport, can cause the rotating drum to rotate out of the locking position, loosening the joint between the panels.
Prior art devices such as these also have the disadvantage that the rotating drum must be fully turned to achieve the "locked" position. This requires accurate positioning of the recess which is to receive the drum in the respective panel. If this recess is positioned too close to the panel edge the panels will butt up against one another before the drum has been turned to the fully locked position and therefore the joint will readily come loose. Alternatively, with the recess too far from the edge of the panel the locked position will be reached before the panels make contact, so that a gap is left between them. The tolerances for positioning the recess are very low; as little as 0.5 mm deviation from the correct position can cause the problems outlined above.
A device intended to overcome these disadvantages is disclosed in U.S. Pat. No. 4,810,127 to Hettich. This fastening device is provided with axially aligned ribs or saw-tooth shaped raised portions on the circumferential surface of the rotating drum, and also has similar raised portions on the inner camming surface of the drum. These formations ensure that unintentional loosening of the fastening device from the locked position is made substantially more difficult, and also provide some facility for locking in positions other than the fully turned position.
The Hettich camming drum does however have some disadvantages, in particular associated with the saw-teeth portions on its outer surface. When the drum is turned more than once or twice in each direction the saw-teeth start to wear away the inner surfaces of the recess in which the drum is placed, and can tend to make the hole oval. The saw-teeth also increases the torque which is required to turn the drum, making it more difficult to turn. The result can be that the drum fells as if it is locked before the joint is secure.
Other problems can arise because of the forces exerted during turning of the rotatable drum. The underside of the head of the pin member and the inner camming surfaces of the drum have been angled, relative to the pin axis, in prior art devices resulting in outwardly directed forces exerted by the pin head on the cam, which can cause bursting of the rotatable drum.
The invention aims to overcome, at least in part, some of the disadvantages of the prior art just described.